Our customer NAM (Nederlandse Aardolie Maatschappij), is an exploration and production company with headquarters in the Netherlands. The 10” x 10,5 km gas pipeline requiring inspection, runs from a sour gas field to the treating plant and is operated at a pressure under 10 bar, which is far below the pressure required for conventional MFL in-line inspection tools.
The common approach would take the pipeline out of service and inspect the pipeline in nitrogen (off-line inspection). Compared a to conventional online inspection significant additional effort is required: Additional coordination and planning, supply of nitrogen equipment, detailed work procedures, risk assessments and additional operators. The impact is not limited to operational costs. Taking it out of service means that production has to be interrupted. NAM approached ROSEN to find a solution for an online inspection.
The challenge in low flow low pressure gas pipelines is not to get the inspection tool through the line but to ensure a constant inspection velocity. The speed excursions which normally occur during the inspection of low flow low pressure conditions are usually caused by obstacles, dents, bends or welds in the line, on which the tools are likely to stop. After a certain time the pressure builds up behind the tool and forces the tool over the obstacle resulting in unwanted speed excursions compromising the data quality.
1. Minimized and constant Friction
As a result of the reduced absolute pressure, a high differential pressure across the inspection tool cannot be realized. The overall friction of the tool therefore needs to be minimized. Ensuring a constant friction during the run further minimizes the unwanted speed variations.
2. Minimized Difference Static/Dynamic Friction
Minimizing the difference between the static and the dynamic friction of the tool reduces the acceleration after tool stops and ensures that the tool velocity returns to normal as quick as possible.
3. Optimized Sealing / Low friction
The sealing capabilities of the tool had to be optimized. A small gap in the seal results immediately in a high loss of flow. All available pressure and flow have to be kept behind the tool.
One key for low-friction is the optimization of the magnetizer. While the brushes serve a valuable purpose of effectively transferring the magnetic flux to the pipe wall, they also add friction. To reduce it in low-pressure pipelines, a special friction reducing magnetizer was developed.
In addition an optimized cup design is equally important to further reducing the friction. The final configuration maximizes the sealing capability while simultaneously ensuring a low and constant friction. The inspection was finally completed in 9 bar pressure and at a velocity of 1.3 m/s. Another benefit of this compact, light weighted tool is that it can be hand carried. No need for cranes and shorter loading – unloading times.
The client benefits were significant:
- Cost effective – no production deferment and no need for an expensive ‘off-line’ inspection in nitrogen
- Flexible – the lines can now be inspected in-service
- Quality – same performance as standard high resolution MFL tools
- Compact – the light weighted tool and handling equipment can be hand carried so cranes are not required anymore and shorted loading – unloading times.
Especially for those lines where a conventional inspection involves high operational cost and/ or production loss, this new LFLP service provides a very attractive alternative.